This invention relates to techniques used as safety equipment for a nuclear reactor and suited for removing decay heat produced in a reactor core at the time of an accident in which a reactor coolant to be supplied into a reactor containment vessel or primary containment vessel is lost.
Examples of reactor safety equipment include the following.
Japanese Patent Unexamined Publication No. 63-191096 proposes a method used in a small- to a medium-size reactor (having an electric power cf up to about 600 MW) so as to statically remove decay heat for a long cooling period after the occurrence of a coolant losing accident, utilizing natural force. More specifically, an outer peripheral pool is provided around the outer periphery of a reactor containment vessel, and the heat inside the reactor containment vessel is transferred to the outer peripheral pool due to a temperature difference between the inside and outside of the reactor containment vessel, and the heat is finally removed from the reactor containment vessel by convection and evaporation of the pool water in the outer peripheral pool. Further, a method was reported in Fall Meeting of the Atomic Energy Society of Japan held in October, 1989, in which a convection promoting plate is provided in water in a pressure control pool in the above reactor containment vessel so as to promote the circulation of this pool water, thereby efficiently radiating the heat of the water of the pressure control pool to the outer peripheral pool via the wall of the reactor containment vessel.
Also, as described in JSME Mechanical Engineer's Handbook C7 (1989), a method is adopted in a large-size reactor (having an electric power of about 1,350 MW), in which a pump and a heat exchanger are used so as to remove decay heat produced in a reactor core in the event of a coolant losing accident.
Any of the above methods effectively removes the heat from the reactor containment vessel to decrease the pressure within the reactor containment vessel.
However, such prior art has the following problems to be solved.
In the method used in the large-size reactor, in addition to the pump and the heat exchanger, auxiliary equipment such as an emergency electricity-generating equipment (energy generating means) for driving the pump is needed for removing the decay heat produced in the reactor core at the time of the coolant losing accident. Therefore, this method has problems that the dynamic equipment is required for removing the decay heat and that the construction is complicated.
On the other hand, the method disclosed in the above Japanese Patent Unexamined Publication No. 63-191096 obviates the need for such dynamic equipment, and therefore the equipment is less liable to a malfunction, which enhances the reliability. However, if this method is adopted directly in the large-size reactor, the heat removal amount per unit area is smaller with this method than with a method using dynamic equipment such as a pump and a heat exchanger. This results in a problem that the reactor containment vessel must be increased in size.